1. Field of the Invention
The present invention relates to a defect correcting method for a liquid crystal panel, which is designed to correct a defect occurring in a manufacturing process of a liquid crystal panel.
2. Description of the Prior Art
Nowadays, the use of a liquid crystal panel is not limited to a display of a portable computer, but has become widespread to various electronic devices including the display of a desktop computer, a television set, the display of a portable terminal, and so on.
A typical Twisted Nematic (TN) liquid crystal panel has a structure where liquid crystal is sealed in between two transparent substrates. On one of the two opposing surfaces of the transparent substrates, a common electrode, color filters, an alignment film and the like are formed. On the other surface, Thin Film Transistors (TFTs), pixel electrodes, an alignment film and the like are formed. Also, polarizing plates are respectively stuck to surfaces opposite the opposing surfaces of the transparent substrates. These two polarizing plates are disposed, for example, so that polarization axes thereof can intersect perpendicularly to each other. When no voltages are applied between the pixel electrode and the common electrode, a light is transmitted to make displaying bright. When a voltage is applied therebetween, a light is shielded to make the displaying dark. When the polarization axes of the two polarizing plates are disposed in parallel to each other, the displaying becomes dark with no voltages applied between the pixel electrode and the common electrode. The displaying becomes bright with a voltage applied therebetween. Hereinafter, the substrate having TFTs and pixel electrodes formed thereon will be referred to as a TFT substrate; and the substrate having color filters and a common electrode formed thereon as a CF substrate.
FIG. 1 is a sectional view showing the structure of a typical TN liquid crystal panel; and FIG. 2 a plan view showing the TFT substrate of the same. FIG. 1 specifically shows a section taken on line Ixe2x80x94I of FIG. 2.
The TN liquid crystal panel comprises: a TFT substrate 10; a CF substrate 20; and liquid crystal 29 sealed in between these TFT and CF substrates 10 and 20.
The TFT substrate 10 is formed in the following process. That is, on a glass substrate 11, a plurality of gate bus lines 12a and a plurality of auxiliary capacitor bus lines 12b are formed to constitute a first wiring layer. Each gate bus line 12a is formed in parallel to another. Between the gate bus lines 12a, an auxiliary capacitor bus line 12b is disposed in parallel thereto.
A first insulating film (gate insulating film, not shown) is formed on these gate and auxiliary capacitor bus lines 12a and 12b. On the first insulating film on the gate bus line 12a, an amorphous silicon film 13 is formed to become a channel of a TFT 15. To constitute a second wiring layer on the first insulating film, a data bus line 14a, and source and drain electrodes 14b and 14c of the TFT 15 are formed. The data bus line 14a is formed to perpendicularly intersect the gate bus line 12a, and the source and drain electrodes 14b and 14c are formed to be separated from each other in both sides of the width direction of the amorphous silicon film 13. The drain electrode 14c is connected to the data bus line 14a. A rectangular region partitioned by the gate bus lines 12a and the data bus lines 14a is a pixel region.
A second insulating film 16 is formed on the data bus line 14a and the source and drain electrodes 14b and 14c. On the second insulating film 16, a transparent pixel electrode 17 made of Indium-Tin Oxide (ITO) is formed. This pixel electrode 17 is electrically connected to the source electrode 14b through a contact hole 16a formed in the second insulating film 16.
On the pixel electrode 17, an alignment film 18 is formed to decide the alignment of liquid crystal molecules. This alignment film 18 made of, e.g., polyimide, has been subjected to alignment treatment by rubbing or the like.
On the other hand, the CF substrate 20 is formed in the following process. That is, on one surface (lower surface in the drawing) of the glass substrate 21, a black matrix 22 made of a light shielding material such as chromium (Cr) is formed to shield a region between pixels and TFTs forming region from lights. In a position opposite to each pixel electrode 17 of the TFT substrate 10, a color filter 23 of one selected from red (R), green (G) and blue (B) is formed. In the described example, color filters 23 of green (G), blue (B) and red (R) are alternately disposed in pixels arrayed in a lateral direction, while color filters of identical colors are disposed in pixels arrayed in a longitudinal direction.
Under the color filters 23, a common electrode 24 made of ITO is formed, and there is an alignment film 25 made of, e.g., polyimide, under this common electrode 24. This alignment film 25 has also been subjected to alignment treatment by rubbing or the like.
Between the TFT substrate 10 and the CF substrate 20, for example spherical or columnar spacers (not shown) uniform in diameter are disposed such that a spacing between these substrates can be kept constant. In addition, polarizing plates (not shown) are respectively disposed on the lower side of the TFT substrate 10 and on the upper side of the CF substrate 20.
In the liquid crystal panel constructed in the foregoing manner, a desired image can be displayed by supplying scanning and video signals from a driving circuit to the gate and data bus lines 12a and 14a at a predetermined timing, and by controlling a voltage between the pixel electrode 17 and the common electrode 24 for each pixel.
In the manufacturing process of a liquid crystal panel, patterning may not be executed correctly because of the sticking of dust or the like, causing short-circuiting or disconnection. Consequently, a pixel may be placed in a constantly lit or unlit state. Usually, in the liquid crystal panel, the presence of dot defects amounting to a predetermined number or smaller is permitted. But when the number is too large, the liquid crystal panel becomes a defective product. In addition, when a plurality of pixel electrodes are connected together, a so-called killer defect occurs, making the liquid crystal panel defective alone.
As regards a method for correcting a dot defect, the prior art has presented a method for welding and joining the electrode of a defective pixel to the gate bus line, the auxiliary capacitor bus line or the data bus line by laser irradiation. When the electrode of the defective pixel is connected to the gate bus line or the auxiliary capacitor bus line, the defective pixel is constantly unlit. Consequently, for example, for white displaying or half-tone displaying, the defective pixel becomes a dark spot to be conspicuous. When the electrode of the defective pixel and the data bus line are connected to each other, any defects cannot be recognized if the same color is displayed on the full surface of a screen. However, when displaying is carried out with the upper half of the screen set white and the lower half thereof set black, if there is a defective pixel in the black portion, it becomes a bright luminescent spot, making a defect conspicuous.
As another method for correcting a dot defect, the prior art has presented a method for disturbing the alignment of liquid crystal molecules by irradiating the entire region of the defective pixel with a laser beam. In this case, a pixel, of which alignment has been disturbed by laser irradiation, is fixed to be black. Thus, as in the case of the connection of the defective pixel electrode to the gate bus line or the auxiliary capacitor bus line, a drawback is inherent, that is, the defective pixel becomes a dark spot in white displaying or half-tone displaying to be conspicuous.
It is an object of the present invention to provide a defect correcting method for a liquid crystal panel, which is capable of preventing a defective pixel, when it occurs, from becoming conspicuous for normal use.
In accordance with an aspect of the present invention, there is provided a defect correcting method for a liquid crystal panel including a plurality of connected pixels, comprising the steps of: electrically cutting off other pixels among the plurality of connected pixels excluding a predetermined pixel from a signal supply line; and driving the other pixels by a signal supplied to the predetermined pixel.
Heretofore, a liquid crystal panel has been put aside as a defective product if a defect of an electrical connection among a plurality of pixels occurs. However, by reducing the number of connections, defective products can be saved.
According to the present invention, when a plurality of pixels are connected, electrical disconnection is made between other pixels excluding a predetermined one among the connected pixels and a signal supply line (data bus line or gate bus line). Accordingly, the plurality of connected pixels are driven by a signal supplied to one pixel. As a result, the number of apparent connections can be reduced by one and, when the number of connections is small, it is not necessary to put aside the panel as a defective product.
When a plurality of adjacent pixels are driven by a signal supplied to one pixel, the other pixels should preferably be driven by a signal supplied to a pixel having a color filter of a high transmittance. This is for the reason that when the plurality of pixels are simultaneously lit, the lighting of a pixel having a low transmittance is inconspicuous, and it is accordingly difficult to recognize a defect.
In accordance with another aspect of the present invention, there is provided a defect correcting method for a liquid crystal panel, comprising the step of: electrically connecting a pixel electrode of a pixel, where a defect has occurred, to a pixel electrode of a pixel having a color filter of a highest light transmittance among adjacent pixels having color filters different in color from the pixel.
According to the present invention, the electrode of a pixel, where a defect has occurred, is electrically connected to that of an adjacent pixel, and the defective pixel is driven simultaneously with the adjacent pixel. In this case, if connection is made to a pixel having a light transmittance lower than that of the pixel having the defect, because of the simultaneous lighting of the two pixels, the defective pixel becomes more conspicuous than a normal pixel. To prevent such an inconvenience, it is necessary to connect the pixel electrode of the defective pixel to that of a pixel having a color filter of a highest light transmittance, among adjacent pixels having color filters different in color from the defective pixel.
In accordance with yet another aspect of the present invention, there is provided a defect correcting method for a liquid crystal panel, comprising the step of: electrically connecting a pixel electrode of a pixel, where a defect has occurred, to a pixel electrode of an adjacent pixel having a color filter identical in color to the defective pixel. Thus, the defect can be made to be inconspicuous.
Furthermore, it is preferable to provide the liquid crystal panel with a correcting wiring beforehand to electrically connect the pixel electrodes of adjacent pixels to each other. Such a correcting wiring is formed on the same wiring layer as that for, e.g., a gate bus line or a data bus line, over pixel regions adjacent to each other.